> I think I recall Lazy.t being defined in 3.04 as = Value of 
> ... | Exception of ... | Suspension of ...
> or something of the sort. Now Lazy.t is defined simply as 
> lazy_t. But what *is* lazy_t exactly?

An abstract type.  You don't want to know :-)  More seriously: in
3.06, the compiler and runtime system represent lazy values more
efficiently; in particular, the "Value of" indirections present in
3.04 are now shortened by the GC whenever possible.  As a consequence,
the representation of lazy values no longer matches that of a Caml datatype.

> Can I apply pattern-matching on it?

No.  The general "contract" of a lazy value is that you should never
have to distinguish whether it's been evaluated already or not.  Just
perform Lazy.force on the lazy value and match on the result.

- Xavier Leroy
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